1. Field of the Invention
The present invention relates to a plasma source for processing an object to be processed (hereinafter referred to as "process target") such as a semiconductor wafer or the like by using plasma, and particularly to a plasma source having a controller for controlling the velocity and direction (vector-control) of constituent particles of plasma such as ions, electrons, radicals (neutral activated elements) or the like in plasma.
2. Description of the Related Art
For example, a plasma CVD (Chemical Vapor Deposition) method, a plasma RIE (Reactive Ion Etching) method, a sputtering method, etc. are known as a processing method using plasma in a semiconductor process. According to these methods, predetermined plasma is produced in a processing chamber while an object (semiconductor wafer) is disposed in the processing chamber, a film is formed on the process target or an etching treatment is performed on the process target by action of plasma constituent particles such as ions, electrons or the like.
Various methods for producing plasma have been hitherto practically used for the above types of plasma sources. At present, new plasma sources for obtaining high-density and uniform plasma under a low process gas pressure have been increasingly studied and developed as disclosed by H. Hara, et al. "Proc. Workshop on Industrial plasma Applications" ISPC-9, 1, pp 62-69 (1989, Italy). However, with these plasma sources, it is impossible to perform the control of the velocity and moving direction of the plasma constituent particles such as reaction gas, ions or the like, and these plasma sources are based on one-dimensional control which is performed on wafers by adjusting a process gas pressure, a plasma potential based on input power, a thermal motion direction, an acceleration of particles in the direction perpendicular to the surface of the semiconductor wafer based on a bias electric field or the like. That is, from a point view of the vector control of plasma, it is the present situation that no vector control is performed by the present plasma sources.
Therefore, the control in the direction perpendicular to the surface of the process target can be performed, that is, the film thickness, the etching depth, etc. on the surface of the process target can be controlled, however, it is difficult to perform the control in the other directions than the direction perpendicular to the surface of the process target. Therefore, the present plasma sources are not suitably applicable to a process for a complicated structure. Accordingly, the conventional plasma sources cannot perform sufficient control in such a process that a trench groove, a Via hole, a contact hole or the like in a semiconductor device is tapered, or in such a process that an oxide film having a desired thickness is coated on the inner surface of the trench groove or the like, and this is a critical problem in a complicated processing work.
Further, a technique for flattening the wafer surface in a wiring process is being increasingly indispensable for the future trends of the micromachining of semiconductor wiring patterns. At present, A CMP (Chemical and Mechanical Polishing) technique is considered for the flattening process. However, a technique for directly and three-dimensionally forming a film into narrow and deep Via holes, trench grooves, contact holes, etc. in a film forming process will be required in the future. However, it is the present situation that the CMP-based method have various problems to be solved, such as productivity, management of dust, contamination, water-proof, and future micromachining.
In view of the foregoing problems, the applicant has invented a novel plasma processing method which can perform plasma control in directions other than the direction perpendicular to the surface of the process target of ions, electrons or the like in plasma, and also perform complicated etching, processing and other works.
According to this method, an electric field is generated in a direction perpendicular to the surface of a process target (semiconductor wafer), and also an electric field is generated in a horizontal direction to the surface, whereby the direction of ions, electrons or the like in plasma is controlled on the basis of the composite electric field of these vertical and horizontal electric fields. This method will be described in detail with reference to FIG. 1.
As shown in FIG. 1, this method controls the moving direction of ions or electrons in plasma 103 generated in a space between an upper electrode 101 and a lower electrode 102 which are disposed in a processing chamber 100. In order to perform the above plasma control, both an electric field E.sub.V which is vertical to the surface of a process target 104 such as a semiconductor wafer or the like (hereinafter referred to as "vertical electric field E.sub.V ") and an electric field E.sub.H which is parallel (horizontal) to the surface of the process object 104 (hereinafter referred to as "horizontal electric field E.sub.H "), are generated simultaneously and combined with each other in a predetermined ratio to generate a composite electric field Ec, and the velocity and moving direction of the ions or electrons in the plasma 103 are controlled by using the composite electric field Ec.
The vertical electric field E.sub.V comprises a plasma sheath electric field which naturally occurs on the surface of the process target 104, a DC bias electric field generated by DC bias 105 applied to the lower electrode 102, and a radio frequency bias electric field generated by radio-frequency bias 106 of 13.56 MHz, for example. Further, the horizontal electric field E.sub.H comprises an induced electric field which is generated, for example, by disposing a pair of coils so that the coils confront both the side portions of the process target 104, supplying an alternating current having a predetermined period into the coils from a single-phase ac power supply to generate a magnetic field in the direction parallel (horizontal) to the surface of the process target 104, and periodically reversing the direction of the magnetic field, whereby the induced electric field is generated so as to surround these magnetic fields.
As described above, according to the previously-proposed plasma control method, the moving direction of ions, electrons or the like in the plasma 103 can be controlled by using the composite electric field Ec comprising the vertical electric field E.sub.V and the horizontal electric field E.sub.H. However, in this method, the vertical electric field E.sub.V is still larger than the horizontal electric field E.sub.H because the vertical electric field is generated on the surface of the process target 104 by the DC bias 105 or radio-frequency bias 106. Therefore, it is difficult to obtain a sufficiently large horizontal electric field E.sub.H, so that the controllability of the composite electric field, that is, the controllability of the velocity and direction of ions, electrons or the like cannot be sufficiently achieved.